This invention relates to a radiation detector, and more particularly to an array type detector for a computerized tomography scanner.
Radiation such as X-rays or .gamma.-rays is used in examination apparatus and measuring apparatus which are employed in medicine, engineering and other fields. To increase the accuracy of examination or measuring, an accurate detection of the dose of radiation is required. Particularly in X-ray computerized tomography (hereinafter abbreviated "CT"), it is necessary for an X-ray detector to accurately detect the intensity of X-rays passing through the living body.
More and more solid-state X-ray detectors are now used in place of gas type X-ray detectors. A gas type X-ray detector has a gaseous photoconductive medium, such as xenon gas, whose conductance varies according to the dose of X-rays passing through it, and so requires an envelope for containing such a gaseous photoconductive medium. The gas X-ray detector which is provided with such an envelope has a complicated structure. Moreover, its X-ray absorption efficiency is low. The X-ray absorption efficiency is influenced by the vibration of the detector and fluctuates by the vibration. By contrast, a solid-state X-ray detector with a semiconductor device is advantageous in several respects. First, it is small and simple. Second, its detector elements can be arranged at short intervals, thus forming a compact array. Third, it has a high X-ray absorption efficiency and can thus detect the dose of X-rays very accurately. Fourth, the relation between the dose of X-rays it receives and an electrical signal it produces is very linear. Fifth, the difference in photosensitivity between the detector elements is small.
Each of the detector elements must, however, be precisely positioned with respect to the incident X-rays. otherwise, the solid-state X-ray detector cannot detect the dose of X-rays accuratley enough to be effectively used in X-ray CT. More specifically, if the axis of each detector element which is a rectangular member is inclined to an incident X-ray, the X-ray will pass through the element along a longer path than otherwise and the element will generate more electron-hole pairs than otherwise, thus producing an erroneous electrical signal.
No solid-state X-ray detector hitherto known has detector elements which are so precisely positioned with respect to incident X-rays and which are so densely arranged as to be effectively employed in an X-ray CT scanner.